1. Field of the Invention
This invention is used primarily in the materials test area to determine fatigue life under various environmental conditions.
More particularly, this invention is directed to a means to measure high pressures during fatigue testing of candidate materials in a hydrogen-rich steam environment. The various candidate materials are subjected to vibratory strain oscillation as well as a high temperature, high pressure environment until they fail.
2. Description of the Prior Art
U.S. Pat. No. 3,095,745 describes a differential pressure instrument which is comprised essentially of two bourdon tubes, each having fixed ends and arranged so that the paths of movement of their free ends lie substantially along parallel lines spaced apart to accommodate a yoke or lever that is mechanically connected to a dial indicator or the like. The free end of one of the tubes moves along a substantially straight line in response to pressure differences, i.e., the motion of the free end thus being approximately rectalinear through a distance which is proportional to the change in pressure between the interior and the exterior of the tube. The tubes are oriented so that the line of movement of each is co-planar and parallel with the line of movement with the other, while the direction of each is opposite to the direction of movement of the other. The instant invention utilizes a pair of identical tubes configured in a substantially sine-like wave pattern, the direction of movement of each tube being the same as opposed to being opposite as is depicted in the foregoing patent. The purpose of the U.S. Pat. No. 3,095,745 patent is to measure the difference between pressure response of a pair of bourdon tubes, while the purpose of the present invention is to measure a single pressure and the differential aspect is only to allow temperature compensation and to facilitate calibration of the transducer without requiring its removal from a high temperature environment. Additionally, the instant invention has the advantage in that its use is particularly adaptable to limited space and high temperature hydrogen-rich steam environments and lends itself to the measurement simultaneously of high pressure while being exposed to a high temperature hydrogen-rich steam environment. A further advantage is the use of multiple bourdon tubes connected in series each one added to an adjacent one, thus accommodating for large displacement while retaining high sensitivity. The foregoing patent does not incorporate these advantages.
In failure testing materials to determine fatigue life under a high temperature hydrogen-rich steam environment, it is necessary to measure the gas pressure inside a specimen containing approximately equal weights of hydrogen gas, and water vapor at pressures up to 7000 psia and temperatures up to 1400.degree. F. If any part of the walls containing the gases should be allowed to cool down to the point where the water vapor condenses to form liquid droplets, most of the water would soon migrate to this particular area of the system, and the relative amount of water vapor in the gas would be depleted. Since the center of the specimen under test is at the highest temperature, the water vapor would migrate away from this region, the very place where the keeping of the proper proportions of hydrogen and water is of the greatest importance. Thus, in the system illustrated, the coolest region should be kept well above the condensation temperature of water. None of the prior art devices are adapted to perform in the foregoing environment. The instant invention avoids this problem because it has no direct internal cooling, therefore, a decided advantage over the prior art is realized.